A generator set (genset) includes a combination of a generator and a prime mover, for example, a combustion engine. As a mixture of fuel and air is burned within the engine, a mechanical rotation is created that drives the generator to produce electrical power. Ideally, the engine drives the generator with a relatively constant torque and speed, and the generator accordingly produces an electrical power output having relatively constant characteristics (frequency, voltage, etc.).
In some applications the electrical power demanded of the genset is greater than can be supplied by a single genset and, thus, multiple gensets are connected in parallel to meet the demands in these situations. Preferably, the power demand remains relatively constant and all available gensets are continuously functional and each produces electrical power at optimum efficiency. However, in practice, the power demand fluctuates as loads are activated and deactivated, thereby requiring the number of gensets online at any given time to vary.
Historically, a single master controller monitored power demand and, based on the demand, either brought additional gensets online or moved them offline to meet the power demand in an efficient manner. Although functionally adequate, the master controller is very expensive and complicated. Thus, a lower cost, simpler alternative is desired.
U.S. Pat. No. 6,639,331 issued to Schultz, on Oct. 28, 2003 (“the '331 patent”) discloses a parallel generator power system for connecting a plurality of generator sets to a common bus. The system includes a separate control module associated with each of the plurality of generator sets. And, in response to a signal to start more than one of the generator sets, each control module initiates operation of its associated generator set. When each of the generator sets is operational and ready for connection to the common bus, each generator set sends a ready-to-load signal to its corresponding control module. The first generator set that sends the ready-to-load signal then also energizes an inhibit line connected between all of the generator sets. By energizing the inhibit line, other generator sets are inhibited from simultaneously connected to the common bus. If multiple generator sets are ready-to-load at the same time, the control modules then arbitrate for the right to send the first start command to their generator set that will result in connection of the generator set to the common bus. In other words, all of the control modules as a whole determine which single one of the modules will allow its generator set to connect to the common bus, while inhibiting other generator sets from connecting to the bus. The arbitration process takes the form of hardware, electronics, and software in each connection module.
Although the system of the '331 patent may provide a way to bring multiple generator sets online in a smooth and controlled manner without the use of a master controller, the system may still be suboptimal. That is, the arbitration process may require significant amounts of time and complex controls that can delay connection of a ready generator set to the common bus. Further, should the first generator set determined to be ready-to-load fail to connect to the common bus, the system of the '331 patent provides no backup strategy.